Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual é a matrícula do STM que está competindo desde 1990?
 ###Tabelas: CREATE TABLE made_both_cuts (made_both_cuts_id AUTO_INCREMENT PRIMARY KEY, Player VARCHAR, Country VARCHAR, Year(s) won VARCHAR, Total INT, To par VARCHAR, Finish VARCHAR) CREATE TABLE participating_schools (participating_schools_id AUTO_INCREMENT PRIMARY KEY, School VARCHAR, Location VARCHAR, Enrolment INT, Founded INT, Denomination VARCHAR, Day/Boarding VARCHAR, School Colours VARCHAR, Abbreviation VARCHAR, In competition since INT) CREATE TABLE officers (officers_id AUTO_INCREMENT PRIMARY KEY, Rank VARCHAR, Badge/Serial Number VARCHAR, Tenure VARCHAR, Date of death VARCHAR, Cause of death VARCHAR) CREATE TABLE doubles_titles (doubles_titles_id AUTO_INCREMENT PRIMARY KEY, Date VARCHAR, Tournament VARCHAR, Surface VARCHAR, Partnering VARCHAR, Opponents in the final VARCHAR, Score VARCHAR) CREATE TABLE wct_1985 (wct_1985_id AUTO_INCREMENT PRIMARY KEY, Date Final VARCHAR, Tournament VARCHAR, Commercial Name VARCHAR, Category VARCHAR, Prize Money/ Surface VARCHAR, Final Match VARCHAR, Semifinal Matches VARCHAR)  
SELECT COUNT Enrolment FROM participating_schools WHERE In competition since = 1990 AND Abbreviation = STM